Providing VPLS-like service over native ATM networks

ABSTRACT

A method and apparatus are provided for emulating VPLS within an ATM network. Provider Edge devices are configured for the VPLS connections. Each provider edge device advertises its configured VPLS IDs to other provider edge devices by propagating an information group up the PNNI hierarchy, the information group containing an association between an ATM address of the provider edge device and the VPLS ID. Information groups are propagated back down the PNNI hierarchy, so that each lowest level node learns all ATM addresses to be associated with each VPLS ID. For each pair of provider edge devices supporting the same VPLS ID, one of the provider edge devices establishes a virtual circuit between the pair. In this way, a mesh of virtual circuits is established between provider edge devices, and a VPLS-like service can be offered to users without having to implement MPLS. The method of advertising ATM addresses can also be applied to other services requiring a number of interconnections between provider edge devices, such as Virtual Private Networks.

FIELD OF THE INVENTION

The invention relates to virtual private LAN services, and moreparticularly to implementation of these services within ATM networks.

BACKGROUND OF THE INVENTION

Virtual Private LAN Service (VPLS) is a proposed standard that wouldallow private local area networks (LANs) to be established over a publicnetwork. The VPLS presents an Ethernet interface to the users. Bridgingis done at Provider Edge devices (PEs), such that the core publicnetwork need not know that a VPLS is being set up. The core network mustsimply guarantee the reachability of the VPLSs between the PEs.

VPLS as currently defined requires that the core network be aMultiProtocol Label Switching (MPLS) network. Once the PEs areconfigured with VPLS identifiers (IDs), the MPLS core network allowsautomatic advertising between the PEs. Each PE advertises to other PEswhich VPLS IDs are supported by the PE, and advertises a MPLS labelwhich other PEs can use to communicate with the PE with respect to eachparticular VPLS ID. As this VPLS ID to MPLS label mapping information isshared among multiple PEs that advertise the same VPLS ID, a mesh ofMPLS label switched paths is generated to interconnect all the PEsinvolved in each VPLS.

Several service providers have already established large AsynchronousTransfer Mode (ATM) networks. In order to implement VPLS (as currentlydefined by the Internet Engineering Task Force) over an ATM network,service providers would have to add an MPLS signaling protocol to theATM network, which would be costly and operationally challenging. Analternative would be to emulate VPLS over an ATM network using a mesh ofvirtual circuits. However, a significant problem for a service providerwishing to emulate VPLS over an existing ATM network is the inability toautomatically establish the mesh of connections between PEs providingthe bridging for the VPLS. ATM nodes advertise reachability informationusing a Private Network-Network Interface (PNNI) routing hierarchy,defined in ATM Forum Technical Committee, “Private Network-NetworkInterface Specification, v.1.1”, af-pnni-0055.002, April 2002. UnderPNNI, each ATM node belongs to a peer group. An ATM node advertises itsreachability information to all nodes within its peer group, but onlythe peer group leader advertises this information outside the peergroup. Furthermore, the information advertised by the peer group leaderto nodes outside the peer group is limited. There is currently no meansby which an ATM node can advertise VPLS ID support to nodes outside itspeer group. This means that an owner of an ATM network cannot offerVPLS-like services to customers, without either tedious manualconfiguration of virtual channels for each pair of PEs and for each VPLSID, or adding an MPLS signaling protocol to the network.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a method is provided foremulating Virtual Provide Local Area Network Service (VPLS) in anAsynchronous Transfer Mode (ATM) network. At a plurality of provideredge devices (PEs) a VPLS having a VPLS Identifier (ID) is configured.Information is exchanged between the PEs indicating a respective ATMaddress at each PE which is associated with the VPLS. For each pair ofPEs, a respective virtual circuit is established between the pair of PEsusing the respective ATM address of each PE as endpoints of the virtualcircuit. If the PEs are arranged in a PNNI hierarchy, the informationindicating a respective ATM address at each PE may be exchanged bygenerating a PNNI Topology State Element (PTSE) including a VPLSinformation group (IG), the VPLS IG indicating the VPLS ID and the ATMaddress to be associated with the VPLS, and flooding each VPLS IGthroughout the PNNI hierarchy. Alternatively, the information may beexchanged by generating a PNNI Augmented Routing (PAR) Service IG, eachPAR Service IG including the VPLS ID and the ATM address to beassociated with the VPLS, and flooding the PAR Service IGs throughoutthe ATM network.

In accordance with another aspect of the invention, a method is providedfor advertising a service having a service ID within an ATM network, theATM network including nodes arranged in a PNNI hierarchy. At each nodewhich supports the service, a PTSE is generated including a service IGindicating the service ID and an ATM address to be associated with theservice. The service IGs are then flooded throughout the PNNI hierarchy.

In accordance with another aspect of the invention, a method is providedfor emulating a VPLS at a provider edge device (PE) within an ATMnetwork. A VPLS ID associated with the VPLS is configured at the PE,including associating an ATM address with the VPLS ID. The associationbetween the VPLS ID and the ATM address is advertised to other nodeswithin the ATM network. The PE determines whether other ATM addresseswithin the ATM network are associated with the VPLS. For each such otherATM address, the PE determines whether the PE is to set up a virtualcircuit with the other ATM address. For each such ATM address with whichthe PE determines it is to set up a virtual circuit, the PE sets up avirtual circuit to the ATM address.

Nodes and logical group nodes are provided for implementing the methodsof the invention.

The method and apparatus of the present invention allow the operator ofan ATM network to emulate VPLS without having to manually configurevirtual circuits between each pair of PEs for each VPLS. By allowingnodes to advertise which VPLS IDs they support, other nodes canestablish virtual circuits to those nodes and a mesh of virtual circuitscan be established automatically. The only configuration needed by theoperator of the network is to configure the VPLS IDs at each node. Theadvertising by the nodes can also be used for other types of mesheswhich can take advantage of automatic connection set-up, such as forLayer 3 or Layer 2 Virtual Private Networks.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following detailed description of the preferred embodiment(s)with reference to the attached figures, wherein:

FIG. 1 is a block diagram of an example communication network;

FIG. 2 is a flow chart of a method by which a Provider Edge device (PE)of FIG. 1 is configured for a VPLS according to one embodiment of theinvention;

FIG. 3 is a flow chart of a method by which a PE of FIG. 1 receives andprocesses VPLS advertisements according to one embodiment of theinvention;

FIG. 4 is a block diagram of the network of FIG. 1 followingestablishment of example VPLS connections according to one embodiment ofthe invention;

FIG. 5 is a block diagram of the network of FIG. 1 followingestablishment of example VPLS connections according to anotherembodiment of the invention; and

FIG. 6 is a diagram of an example set of nodes arranged in a PNNIhierarchy.

It will be noted that in the attached figures, like features bearsimilar labels.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a block diagram of an example communication networkis shown. The communication network has an Asynchronous Transfer Mode(ATM) network 10 as a core network. The ATM network 10 includes threeProvider Edge devices (PEs), PE1, PE2, and PE3, and guaranteesreachability between each pair of PEs. Each PE provides at least oneCustomer Premises Equipment device (CPE) with communication access tothe ATM network 10. In the example network of FIG. 1, PE1 providescommunication access to CPE1 and CPE2, PE2 provides communication accessto CPE3 and CPE4, and PE3 provides communication access to CPE5. CPE1and CPE3 belong to a first Virtual Private LAN Service (VPLS) having aVPLS identifier (ID) of 1. CPE2, CPE4, and CPE5 belong to a second VPLShaving a VPLS ID of 2.

The network described with reference to FIG. 1 is for the purposes ofexample only. More generally, there are at least two PEs, each of whichprovides at least one CPE with communication access to the ATM network10. The network supports at least one VPLS, at least two CPEs belongingto each VPLS. Not all CPEs on a PE need belong to a VPLS.

Broadly, a VPLS is established over the ATM network 10 by configuringeach PE supporting the VPLS with the VPLS ID, exchanging between the PEsthe ATM addresses associated by each PE with the VPLS, and establishinga mesh of virtual circuits interconnecting each pair of PEs supportingthe VPLS.

Referring to FIG. 2, a method by which each PE of FIG. 1 is configuredfor a VPLS according to one embodiment of the invention is shown. Atstep 20, a PE is configured to support a VPLS of at least one CPE forwhich the PE provides communication access to the network 10. In thenetwork of FIG. 1, PE1 is first configured to support VPLS ID 1. TheVPLS has a VPLS ID which is allocated a unique ATM address at the PE,and at step 22 the PE advertises the VPLS ID and the associated ATMaddress to other PEs within the network 10. The association between aVPLS ID and an ATM address will be referred to herein as a VPLS IDmapping, and can take any form. One method by which the PE advertisesVPLS ID mappings is described below with reference to FIG. 6.

At step 24 the PE determines whether the VPLS ID is supported by anyother PEs. For example, the PE may consult a database of VPLS IDmappings it has received from other PEs. The PE may conclude that theVPLS ID is not supported by any other PEs if the PE was the first PE tobe configured for the VPLS ID, or if a second PE has been configured forthe VPLS ID but the VPLS ID mapping advertised by the second PE has notyet reached the present PE. If the PE determines that the VPLS ID is notsupported by any other PEs, then the PE enters a wait state 26. From thewait state 26, another VPLS ID can be configured at step 20, for exampleVPLS ID 2 for PE1.

If at step 24 the PE determines that the VPLS ID is supported by asecond PE, then a new virtual circuit needs to be established betweenthe PE and the second PE. However, since virtual circuits arebi-directional, only one of the PE and the second PE should set up avirtual circuit. At step 28 the PE determines whether it is to be aninitiator of the virtual circuit. This may be determined using anymethod guaranteed to indicate to exactly one of the PE and the second PEthat it is to be the initiator of the virtual circuit, when the methodis executed by both the PE and the second PE. For example, the methodcould determine that the PE having the lower address is to be theinitiator of the virtual circuit.

If the PE determines at step 28 that it is not to be the initiator ofthe virtual circuit, then the PE determines whether there are anyadditional PEs which support the VPLS ID at step 24. If the PEdetermines at step 28 that it is to be the initiator of the virtualcircuit, then at step 30 the PE sets up a virtual circuit between the PEand the second PE, using the ATM address which the second PE hasassociated with the VPLS ID as the destination of the virtual circuit.The ATM address to be used as the destination of the virtual circuit isdetermined from the VPLS ID mapping advertised by the second PE. Oncethe virtual circuit is set up, then VPLS traffic between the PE and thesecond PE can be carried over the virtual circuit for traffic associatedwith the VPLS ID. The PE then determines whether there are anyadditional PEs which support the VPLS ID at step 24.

As stated above, a PE may be configured and may advertise its VPLS IDmapping before it becomes aware of any other PEs which support the VPLSID. Referring to FIG. 3, a method by which the PE receives and processesinformation identifying ATM addresses to be associated with a VPLS IDaccording to one embodiment of the invention is shown. At step 40 the PEreceives a VPLS ID mapping, the VPLS ID mapping being any form ofinformation indicating an association between an ATM address and a VPLSID, as a result of a second PE having advertised its support of a VPLSID as described above with reference to step 22 of FIG. 2. For example,the second PE may have advertised a VPLS ID mapping as described belowwith reference to FIG. 6 during configuration of the second PE. The VPLSID mapping includes a VPLS ID and an associated ATM address.

At step 42 the PE stores the VPLS ID mapping. This is necessary becausethe VPLS ID may not yet be supported at the PE. If the PE is configuredfor this VPLS ID at a later time, then the PE will know at that timethat a virtual circuit needs to be established between itself and asecond PE, as described above with reference to step 24 of FIG. 2.

At step 44 the PE determines whether the VPLS ID of the VPLS ID mappingis one for which the PE is already configured. If the VPLS ID is not onefor which the PE is already configured, then there is no need for avirtual circuit between the PE and the second PE, and the PE enters await state 46. For example, the VPLS ID mapping could have been receivedby PE3 of FIG. 1 from PE2, indicating an ATM address to be associatedwith VPLS ID 1.

If the PE determines at step 44 that the VPLS ID of the VPLS ID mappingis one for which the PE is already configured, then a virtual circuitneeds to be set up between the PE and the second PE so that trafficassociated with that VPLS can be communicated between the PE and thesecond PE. The PE determines at step 28 whether the PE is to be aninitiator of the virtual circuit, as described above with reference toFIG. 2. If the PE is not to be the initiator of the virtual circuit,then the PE enters the wait state 46. If the PE is to be the initiatorof the virtual circuit, then at step 30 the PE sets up a virtual circuitbetween the PE and the second PE, as described above with reference toFIG. 2. Once the virtual circuit is set up, then VPLS traffic betweenthe PE and the second PE can be carried over the virtual circuit fortraffic associated with the VPLS ID. The PE then enters the wait state46.

It should be noted that the PE may receive (or learn of) more than oneVPLS ID mapping at step 40, in which case the PE stores the associationbetween ATM address and VPLS ID indicated by each VPLS ID mapping. Forthe sake of clarity, a single message containing more than one VPLS IDmapping is viewed logically as multiple advertisements of individualVPLS ID mappings, each VPLS ID mapping being processed in a separateloop of the wait state 46 and the step 40 of receiving a VPLS IDmapping.

Each PE includes a VPLS controller (not shown in FIG. 1). The VPLScontroller comprises instructions for allowing configuration of a VPLSat the PE, and for receiving and processing VPLS ID mappings. In thepreferred embodiment, the instructions are in the form of softwarerunning on a processor, but may more generally be in the form of anycombination of software or hardware within a processor, includinghardware within an integrated circuit. The processor need not be asingle device, but rather the instructions could be located in more thanone device. If in the form of software, the instructions could be storedon a computer-readable medium.

Referring to FIG. 4, the network of FIG. 1 is shown followingestablishment of a mesh of interconnections in order to emulate VPLSfollowing configuration and exchange of VPLS ID mappings as describedabove with reference to FIG. 2 and FIG. 3. A first virtual circuit 50has been established between PE1 and PE2 for carrying traffic associatedwith VPLS ID 1. A second virtual circuit 52 has been established betweenPE1 and PE2 for carrying traffic associated with VPLS ID 2. A thirdvirtual circuit 54 has been established between PE1 and PE3 for carryingtraffic associated with VPLS ID 2. A fourth virtual circuit 56 has beenestablished between PE2 and PE3 for carrying traffic associated withVPLS ID 2. All virtual circuits are bi-directional.

The methods of FIG. 2 and FIG. 3 have been described with each VPLS IDbeing associated with a unique ATM address. In an alternativeembodiment, each PE may assign a single ATM address to more than one, oreven all, VPLS IDs supported by the PE. In such an embodiment, the step30 of setting up a virtual circuit between two PEs would require thatthe VPLS ID be included in the virtual circuit set-up signaling aseither a separate information element (IE) or as part of an existing IE.Referring to FIG. 5, the network of FIG. 1 is shown followingestablishment of a mesh of interconnections in order to emulate VPLSfollowing configuration and exchange of advertisements in the embodimentin which each PE assigns a single ATM address to more than one VPLS ID.The mesh of virtual circuits is similar to that shown in FIG. 4, but thetwo virtual circuits 50 and 52 have been established by signaling theindividual VPLS IDs 1 and 2 in both virtual circuits while they arebeing established. This allowed the receiver of the setup message toattach the virtual circuit to the correct VPLS ID on either PE.Including the VPLS ID in the setup message allows the destination PE todetermine for which CPE or CPEs the virtual circuit is to be associatedso traffic can be sent to the correct CPE.

Referring to FIG. 6, an example Private Network-Network Interface (PNNI)hierarchy of nodes within the ATM network 10 of FIG. 1 is shown. Lowestlevel nodes A.1.1, A.1.2, and A.1.3, form a peer group PG(A.1), A.1.3being the peer group leader. Lowest level nodes A.2.1, A.2.2, and A.2.3form a peer group PG(A.2), A.2.2 being the peer group leader. Lowestlevel node B.1 forms a peer group PG(B), and is the peer group leader.Logical group nodes A.1 and A.2 form logical group PG(A), of which A.2is the peer group leader. Logical group nodes A and B form a highestlevel peer group 70. Lowest level nodes A.1.1, A.2.1, A.2.3, and B.1 areconfigured to support a common VPLS. Each of the PEs of FIG. 1 would bea lowest level node within the PNNI hierarchy of FIG. 6, and if thecommon VPLS corresponded to VPLS ID 2, each of the PEs of FIG. 1 wouldbe one of lowest level nodes A.1.1, A.2.1, A.2.3, and B.1.

In order to establish a mesh of virtual circuits to support the commonVPLS, virtual circuits must be established between lowest level nodesA.1.1, A.2.1, A.2.3, and B.1, as described above with reference to FIG.2 and FIG. 3. Each lowest level node supporting a VPLS must advertisethis support, as indicated above with reference to step 22 of FIG. 2. Inone embodiment of the invention, a new PNNI Topology State Element(PTSE) information group (IG) is defined for PNNI routing. Each lowestlevel node includes within PTSEs it advertises to its peer group a VPLSIG indicating a VPLS ID and an associated ATM address. One such VPLS IGis included for each VPLS ID supported by the node. Within each peergroup (PG), the peer group leader (PGL) receives all PTSEs floodedthroughout the PG. In addition to the standard PNNI summarization, thePGL extracts the VPLS IGs from the PTSEs, each VPLS IG identifying aVPLS ID mapping for a VPLS ID supported by a lowest level node withinthe PG. The PGL propagates the VPLS IGs up the hierarchy to its parentnode via the logical group node of the PG.

Each logical group node may receive VPLS IGs from its respective PGL.Each logical group node floods these VPLS IGs throughout its own PG. ThePGL of each higher level PG receives the VPLS IGs from all logical groupnodes within the higher level PG, and propagates the VPLS IGs up thehierarchy to the next highest level logical group node. This repeatsuntil the highest level group is reached, at which point all VPLS IGshave been propagated up the PNNI hierarchy. In this embodiment, the VPLSIGs provide the VPLS ID mappings advertised by the PEs (described abovewith reference to step 22 of FIG. 2) and received by the PEs (describedabove with reference to step 40 of FIG. 3).

In the example hierarchy of FIG. 6, if the common VPLS ID is “10” thenthe logical group node A.1 maintains the VPLS ID mapping “10, A.1.1” andpasses it as a VPLS IG to LGN A.2 (the only other logical group node inits peer group). The logical group node A.2 maintains the VFLS IDmappings “10, A.2.1” and “10, A.2.3” and passes them as VPLS IGs tological group node A.1. The logical group node A maintains the VPLS IDmappings “10, A.1.1”, “10, A.2.1” and “10, A.2.3” and passes them asVPLS IGs to logical group node B. The logical group node B maintains theVPLS ID mapping “10, B.1” and passes it as a VPLS IG to logical groupnode A.

As with conventional PTSE flooding, each logical group node thatreceives mappings floods the PTSEs to each logical group node or lowestlevel node in its child peer group. In this way, the mappings are passedback down the hierarchy to the lowest level nodes. For example, logicalgroup node A passes VPLS ID mapping “10, B.1” to the nodes within peergroup A, namely logical group nodes A.1 and A.2. Logical group node Adoes not pass the VPLS ID mappings “10, A.1.1”, “10, A.2.1”, and “10,A.2.3” to logical group node A.1 and A.2 as these two logical groupnodes are already aware of these VPLS ID mappings. Logical group nodeA.1 passes the VPLS ID mappings “10, A.2.1”, “10, A.2.3”, and “10, B.1”to the lowest level nodes within peer group A.1, namely lowest levelnodes A.1.1, A.1.2, and A.1.3.

In this way, each lowest level node learns of the ATM addresses of allother nodes supporting the common VPLS ID. Upon receipt of these VPLS IDmappings, each lowest level node stores the mappings and determineswhether it should establish a virtual circuit to the ATM addresseslisted in the mappings, as described above with reference to FIG. 3.

In one embodiment, each lowest level node configured for a VPLS alsoincludes in the VPLS ID mappings (such as within a VPLS IG within aPTSE) one or more traffic characteristics of traffic that will becarried within the VPLS. This may be required if a node foresees limitedresources. A second node that receives a VPLS ID mapping will note thetraffic characteristics within the VPLS ID mapping. If the second nodeis the initiator of the virtual circuit between the two nodes, then thesecond node will set up a virtual circuit between the two nodes whichwill satisfy only the minimum traffic characteristics as specified byeach node. For example, if the first node advertises 100 Mbits capacityfor a VPLS ID and the second node advertises 10 Mbits capacity for thesame VPLS ID, then the node which sets up the virtual circuit betweenthe nodes for the VPLS ID will set up a virtual circuit having acapacity of 10 Mbits, irregardless of which node actually is responsiblefor setting up the virtual circuit.

The use of IGs indicating VPLS ID mappings to allow nodes to exchangeATM addresses to be associated with a service ID can be used for anyservice requiring interconnections between nodes where each instance ofthe service has an associated identifier. Each node advertises anassociation between a service ID and an ATM address by including an IGidentifying the association within a PTSE flooded throughout the node'speer group, and subsequently throughout the PNNI hierarchy. This allowsvirtual circuits to be established automatically, as described above foremulation of VPLS. For example, if a Virtual Private Network needs to beestablished, then each lowest level node includes in its PTSE an IGindicating an association between a VPN ID of the VPN and an ATM addressto be associated with the VPN. As other nodes learn that the nodesupports the specified VPN at the specified ATM address, virtualcircuits can be set up between pairs of nodes supporting the VPN.

In another embodiment, the advertising by PEs of support for VPLS IDs,as described broadly above with reference to step 22 of FIG. 2 and step40 of FIG. 3, is accomplished by a modification to PNNI AugmentedRouting (PAR), the conventional implementation of which is described inaf-ra-0104.000, “PNNI Augmented Routing (PAR) Version 1.0”, The ATMForum Technical Committee, January 1999. In this embodiment, each PEgenerates a PAR Service IG according to conventional PAR, but populatesthe PAR Service IG with the ATM address of which the PE is associatingwith the VPLS ID. The PE then nests a conventional PAR VPN ID IG withinthe PAR Service IG, but populates the PAR VPN ID IG with the VPLS ID.The PAR Service IG thereby includes the VPLS ID mapping, the ATM addressportion of the VPLS ID mapping being within the PAR Service IG itselfand the VPLS ID portion of the VPLS ID mapping being within the PAR VPNID IG nested within the PAR Service IG. A new VPLS VPN IG may also bedefined by the PE and nested within the PAR VPN ID IG. The VPLS VPN IGis similar in function to the existing PAR IPv4 Service Definition IG,and includes information such as traffic descriptor information (asdescribed above) or any other VPLS-specific information. Other encodingsof the VPLS ID mapping are possible, such as embedding the VPLS ID inthe VPLS VPN IG rather than in a PAR VPD ID IG.

At step 22 of FIG. 2, the PE advertises the VPLS ID mapping bypropagating the PAR Service IG throughout the PNNI hierarchy usingconventional PAR flooding methods. At step 40 of FIG. 3, a PE whichreceives a PAR Service IG extracts the VPLS ID mapping from the PARService IG.

In the embodiment in which PAR is used to advertise VPLS ID mappingsbetween PEs, not all PEs need run the PNNI routing protocol.Alternatively, at least one PE can be attached to the ATM network via anATM link running a signaling protocol such as ATMF UNI or ATMF AINIsignaling, and exchange VPLS ID mappings with other PEs using Proxy PAR(described in Section 5 of af-ra-0104.000, “PNNI Augmented Routing (PAR)Version 1.0”, The ATM Forum Technical Committee, January 1999). Thisallows PEs to advertise their VPLS ID mappings and receive the VPLS IDmappings of other PEs, thereby permitting establishment of the mesh ofvirtual circuits between PEs supporting a common VPLS ID, but withoutrequiring that every PE run the full suite of PNNI routing and signalingprotocols. Use of Proxy PAR also allows connectivity between anycombination of PEs running PNNI (and PAR) and PEs that run Proxy PARinstead of PNNI.

The embodiments presented are exemplary only and persons skilled in theart would appreciate that variations to the embodiments described abovemay be made without departing from the spirit of the invention. Methodslogically equivalent or similar to the methods described above withreference to FIG. 2 and FIG. 3 are within the scope of the invention.The scope of the invention is solely defined by the appended claims.

1. A method of emulating Virtual Provide Local Area Network Service(VPLS) in an Asynchronous Transfer Mode (ATM) network, comprising thesteps of: configuring at a plurality of provider edge devices (PEs) aVPLS having a VPLS Identifier (ID); exchanging information between thePEs indicating a respective ATM address at each PE which is associatedwith the VPLS; and for each pair of PEs, establishing a respectivevirtual circuit between the pair of PEs using the respective ATM addressof each PE as endpoints of the virtual circuit.
 2. The method of claim 1wherein at each PE, the respective ATM address associated with the VPLSis unique to the VPLS.
 3. The method of claim 1 wherein a second VPLS isemulated at a plurality of the PEs, and wherein at each such PE therespective ATM address associated with the VPLS is also associated withthe second VPLS.
 4. The method of claim 1 wherein the PEs are arrangedin a Private Network-Network Interface (PNNI) hierarchy, and wherein thestep of exchanging information between the PEs comprises the steps of:at each PE, generating a PNNI Topology State Element (PTSE) including aVPLS Information Group (IG), the VPLS IG indicating the VPLS ID and theATM address to be associated with the VPLS; and flooding each VPLS IGthroughout the PNNI hierarchy.
 5. The method of claim 4 wherein the stepof flooding each VPLS IG throughout the PNNI hierarchy comprises thesteps of: at each PE, flooding the PTSE throughout a peer group of thePE, each peer group having a peer group leader; at each peer groupleader, receiving each PTSE generated by a PE within the peer group ofthe peer group leader and flooding such PTSEs throughout a parentlogical group of the peer group leader; at each peer group leader,receiving at least one other PTSE, each other PTSE containing a VPLS IGindicating an association between the VPLS ID and an ATM address, fromthe parent logical group of the peer group leader; and at each peergroup leader, flooding the at least one other PTSE throughout the peergroup of the peer group leader.
 6. The method of claim 1 wherein thestep of exchanging information between the PEs comprises the steps of:at each PE, generating a PNNI Augmented Routing (PAR) Service IGincluding the VPLS ID and the ATM address to be associated with theVPLS; and flooding each PAR Service IG throughout the ATM network. 7.The method of claim 6 wherein at least one other PE uses Proxy PAR toexchange with PEs ATM addresses to be associated with the VPLS.
 8. Themethod of claim 7 wherein the at least one other PE is attached to theATM network via an ATM link employing an ATM User Network Interface(UNI) signaling protocol.
 9. The method of claim 7 wherein the at leastone other PE is attached to the ATM network via an ATM link employing anATM Inter-Network Interface (AINI) signaling protocol.
 10. A method ofadvertising a service having a service identifier (ID) within anAsynchronous Transfer Mode (ATM) network, the ATM network including aplurality of nodes arranged in a Private Network-Network Interface(PNNI) hierarchy, the method comprising the steps of: at each node whichsupports the service, generating a PNNI Topology State Element (PTSE)including a service Information Group (IG), the service IG indicatingthe service ID and an ATM address to be associated with the service; andflooding each PTSE throughout the PNNI hierarchy.
 11. The method ofclaim 10 wherein the step of flooding each PTSE throughout the PNNIhierarchy comprises: at each PE, flooding the PTSE throughout a peergroup of the PE, each peer group having a peer group leader; at eachpeer group leader, receiving each PTSE generated by a PE within the peergroup of the peer group leader and flooding such PTSEs throughout aparent logical group of the peer group leader; at each peer groupleader, receiving at least one other PTSE, each other PTSE containing aservice IG indicating an association between the service ID and an ATMaddress, from the parent logical group of the peer group leader; and ateach peer group leader, flooding the at least one other PTSE throughoutthe peer group of the peer group leader.
 12. A method of emulating aVirtual Private Local Area Network Service (VPLS) at a Provider Edgedevice (PE) within an Asynchronous Transfer Mode (ATM) network,comprising the steps of: configuring at the PE a VPLS Identifier (ID)associated with the VPLS, including associating an ATM address with theVPLS ID; advertising the association between the VPLS ID and the ATMaddress to other nodes within the ATM network; determining other ATMaddresses within the ATM network which are associated with the VPLS; foreach such other ATM address, determining whether the PE is to set up avirtual circuit with the ATM address; and for each such other ATMaddress with which the PE determines that the PE is to set up a virtualcircuit, setting up a virtual circuit with the other ATM address. 13.The method of claim 12 wherein the step of advertising the associationbetween the VPLS ID and the ATM address further comprises advertising atleast one traffic characteristic to be associated with the VPLS ID andthe ATM address.
 14. The method of claim 13 wherein the step of settingup a virtual circuit comprises setting up the virtual circuit inconformance with the at least one traffic characteristic.
 15. The methodof claim 12 wherein the node is part of a Private Network-NetworkInterface (PNNI) hierarchy, and wherein the step of advertising theassociation between the VPLS ID and the ATM address to other nodeswithin the VPLS comprises the steps of: generating a PNNI Topology StateElement (PTSE) including a VPLS information group (IG), the VPLS IGindicating the VPLS ID and the ATM address associated with the VPLS; andflooding the PTSE throughout the peer group of the node.
 16. The methodof claim 12 wherein the step of advertising the association between theVPLS ID and the ATM address comprises the steps of: generating a PrivateNetwork-Network Interface (PNNI) Augmented Routing (PAR) Serviceinformation group (IG) including the VPLS ID and the ATM address; andflooding the PAR Service IG throughout the ATM network.
 17. A nodewithin an Asynchronous Transfer Mode (ATM) network, comprising: meansfor receiving a Virtual Private Local Area Network Service (VPLS)identifier (ID); and a VPLS controller comprising: instructions forassociating an ATM address with the VPLS ID; instructions foradvertising the association between the ATM address and the VPLS ID toother nodes within the ATM network; instructions for determining otherATM addresses within the ATM network which are associated with the VPLSID; instructions for, for each such other ATM address, determiningwhether the node is to set up a virtual circuit with the other ATMaddress; and instructions for, for each such other ATM address that thenode determines that the node is to set up a virtual circuit, setting upa virtual circuit with the other ATM address.
 18. The node of claim 17wherein the node is part of a Private Network-Network Interface (PNNI)hierarchy, and wherein the instructions for advertising the associationbetween the ATM address and the VPLS ID comprise: instructions forgenerating a PNNI Topology State Element (PTSE) including a VPLSinformation group (IG), the VPLS IG indicating the VPLS ID and the ATMaddress associated with the VPLS; and instructions for flooding the PTSEthroughout a peer group of the node.
 19. The node of claim 17 whereinthe node is part of a Private Network-Network Interface (PNNI)hierarchy, and wherein the instructions for advertising the associationbetween the ATM address and the VPLS ID comprise: instructions forgenerating a PNNI Augmented Routing (PAR) Service information group(IG), the PAR service IG including the VPLS ID and the ATM address to beassociated with the VPLS; and instructions for flooding the PAR serviceIG throughout the ATM network.
 20. The node of claim 17 wherein theinstructions for advertising the association between the ATM address andthe VPLS ID comprise instructions for delivering the association to asecond node using Proxy PAR.
 21. A node within an Asynchronous TransferMode (ATM) network, the node being part of a Private Network-NetworkInterface (PNNI) hierarchy within the ATM network and comprising:instructions for receiving a service identifier (ID) identifying aservice; instructions for generating a PNNI Topology State Element(PTSE) including a service information group (IG), the service IGindicating the service ID and an ATM address to be associated with theservice; and instructions for flooding the service IG throughout thePNNI hierarchy.
 22. A logical group node within a PrivateNetwork-Network Interface (PNNI) hierarchy in an Asynchronous TransferMode (ATM) network, the logical group node having a peer group and achild peer group, and comprising: instructions for receiving at leastone PNNI Topology State Element (PTSE) from nodes within the child peergroup, each PTSE including a Virtual Private Local Area Network Service(VPLS) information group (IG), each VPLS IG indicating an associationbetween a VPLS identifier (ID) and an ATM address; instructions forflooding each of the at least one PTSE throughout the peer group;instructions for receiving at least one other PTSE from other logicalgroup nodes within the peer group, each PTSE including a VPLS IGindicating an association between the VPLS ID and an ATM address;instructions for flooding each of the at least one other PTSE throughoutthe child peer group.